This invention relates to a trap for hydrocarbon vapors for use with plastic extruders.
In plastic extruders discharge vapors are pulled by a vacuum pump from the extruder just prior to the ejection of the hot plastic material from the extruder. If no trap is provided to catch the hydrocarbons which are included in the discharge vapors, either the hydrocarbons condense from the vapor stream and clog the discharge valve, or the vapors may be charged to the air causing an increase in potentially harmful hydrocarbon effluent in the work area, or the vapors may be dissolved into the water of the vacuum pump to pollute it and cause a problem in the disposal of that water. In addition, the vapor discharge often includes expensive additives such as plastic stabilizers which, if collected, could be saved and reused.
Other vapor traps have been employed, but they are not efficient and require continual attention, such as emptying the trap or unclogging the conduit into the vacuum pump. Some traps, for example, have to be emptied at least every thirty minutes. The conduits into the vacuum pump, in some installations, must be cleared on an equally frequent basis. This presents a disruption in the use of the extruder, and requires a worker to keep a constant eye on the vapor trap, vacuum pump, and related system.
It is an advantage to provide a vapor trap which allows for the proper cooling steps and dwell time to cause hydrocarbon vapors to condensate from a discharge stream in a sump area of the vapor trap, leaving the extruder discharge pipe or conduit free from clogging.
The trap must allow for the removal of the thick hydrocarbon condensate, but still be able to withstand a relatively high vacuum. It is an additional advantage if the trap can be emptied by a single worker, and if the worker can reconnect the trap by himself after the trap has been emptied.